LSP & Completion

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Overview

• nvim-lspconfig: LSP client configuration
• mason.nvim: LSP server installation manager
• nvim-cmp: Completion engine
• LuaSnip: Snippet engine
• Multiple completion sources: LSP, buffer, path, snippets
• lspkind: VSCode-like completion icons

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Completion Engine: nvim-cmp

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Features

• Multiple Sources: Combines LSP, snippets, buffer text, and file paths
• Smart Sorting: Prioritizes relevant completions
• Preview: Shows documentation for completion items
• Snippet Support: Expands and navigates snippets
• LSP Integration: Full support for LSP capabilities

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Completion Sources

1. nvim_lsp: Completions from language servers
2. luasnip: Snippet completions
3. buffer: Text from current buffer
4. path: Filesystem paths

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Keybindings

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In Completion Menu

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Completion Behavior

completion = {
  completeopt = "menu,menuone,preview,noselect",
}

• menu: Show popup menu
• menuone: Show menu even for single match
• preview: Show preview window with documentation
• noselect: Don’t auto-select first item

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Configuration

return {
  "hrsh7th/nvim-cmp",
  event = "InsertEnter",
  dependencies = {
    "hrsh7th/cmp-buffer",
    "hrsh7th/cmp-path",
    "L3MON4D3/LuaSnip",
    "saadparwaiz1/cmp_luasnip",
    "rafamadriz/friendly-snippets",
    "onsails/lspkind.nvim",
  },
  config = function()
    local cmp = require("cmp")
    local luasnip = require("luasnip")
    local lspkind = require("lspkind")

    -- Load VSCode-style snippets
    require("luasnip.loaders.from_vscode").lazy_load()

    cmp.setup({
      snippet = {
        expand = function(args)
          luasnip.lsp_expand(args.body)
        end,
      },
      mapping = cmp.mapping.preset.insert({
        ["<C-k>"] = cmp.mapping.select_prev_item(),
        ["<C-j>"] = cmp.mapping.select_next_item(),
        ["<C-b>"] = cmp.mapping.scroll_docs(-4),
        ["<C-f>"] = cmp.mapping.scroll_docs(4),
        ["<C-Space>"] = cmp.mapping.complete(),
        ["<C-e>"] = cmp.mapping.abort(),
        ["<CR>"] = cmp.mapping.confirm({ select = false }),
      }),
      sources = cmp.config.sources({
        { name = "nvim_lsp" },
        { name = "luasnip" },
        { name = "buffer" },
        { name = "path" },
      }),
      formatting = {
        format = lspkind.cmp_format({
          mode = "symbol_text",
        }),
      },
    })
  end,
}

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Snippet Engine: LuaSnip

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Features

• VSCode Snippets: Compatible with VSCode snippet format
• Dynamic Snippets: Snippets can execute Lua code
• Snippet Navigation: Tab through snippet placeholders
• Friendly Snippets: Includes large snippet library

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Snippet Sources

• friendly-snippets: Community-maintained snippet collection
  • Snippets for 50+ languages
  • Common patterns and boilerplate
  • Framework-specific snippets (React, Vue, etc.)

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Usage

1. Start typing snippet trigger
2. Snippet appears in completion menu
3. Press <CR> to expand
4. Tab through placeholders
5. Finish editing snippet

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Example Snippets

• log → console.log()
• cl → console.log()
• fn → function declaration
• afn → arrow function
• imp → import statement

• def → function definition
• class → class definition
• if → if statement
• for → for loop

• ! → HTML5 boilerplate
• div → <div></div>
• link → <link> tag

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Completion Icons: lspkind

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Icon Types

• 󰊕 Method
• 󰆧 Function
• 󰀫 Variable
• Class
• ⌘ Keyword
• Snippet
• File
• Folder

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Format

󰊕 methodName (method)
 myVariable (variable)

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Completion Sources

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LSP Source (cmp-nvim-lsp)

• Function and method names
• Variable names
• Class and interface names
• Keywords
• Import suggestions

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Buffer Source (cmp-buffer)

• Words you’ve already typed
• Variable names in current file
• Useful when LSP isn’t available

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Path Source (cmp-path)

• File paths
• Directory paths
• Relative and absolute paths

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Snippet Source (cmp_luasnip)

• Pre-defined snippets
• Custom snippets
• Framework-specific patterns

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LSP Configuration: nvim-lspconfig

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Features

• Go to Definition: Jump to symbol definitions
• Find References: Find all references to a symbol
• Hover Documentation: Show documentation for symbol under cursor
• Code Actions: Quick fixes and refactorings
• Diagnostics: Real-time error and warning detection
• Auto-format: Format code on save

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Auto-format on Save

vim.api.nvim_create_autocmd("BufWritePre", {
  pattern = { "*.js", "*.ts" },
  callback = function()
    vim.lsp.buf.format({ async = true })
  end,
})

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Configuration

return {
  {
    "hrsh7th/cmp-nvim-lsp",
    event = { "BufReadPre", "BufNewFile" },
    dependencies = {
      { "antosha417/nvim-lsp-file-operations", config = true },
      { "folke/lazydev.nvim", opts = {} },
      { "neovim/nvim-lspconfig" },
    },
    config = function()
      local cmp_nvim_lsp = require("cmp_nvim_lsp")
      
      -- Enable autocompletion for LSP
      local capabilities = cmp_nvim_lsp.default_capabilities()
      
      -- Auto-format on save
      vim.api.nvim_create_autocmd("BufWritePre", {
        pattern = { "*.js", "*.ts" },
        callback = function()
          vim.lsp.buf.format({ async = true })
        end,
      })
    end,
  },
}

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Package Manager: mason.nvim

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Features

• Easy Installation: Install servers with simple commands
• Cross-platform: Works on Windows, macOS, and Linux
• Auto-install: Can automatically install configured servers
• Version Management: Install specific versions of tools

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UI Commands

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UI Icons

• ✓ Package installed
• ➜ Package pending installation
• ✗ Package not installed

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Configuration

return {
  {
    "williamboman/mason.nvim",
    opts = {
      ui = {
        icons = {
          package_installed = "✓",
          package_pending = "➜",
          package_uninstalled = "✗",
        },
      },
    },
  },
}

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Mason LSP Config: mason-lspconfig.nvim

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Auto-installed Servers

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Configuration

return {
  {
    "williamboman/mason-lspconfig.nvim",
    opts = {
      ensure_installed = {
        "ts_ls",
        "html",
        "cssls",
        "tailwindcss",
        "svelte",
        "lua_ls",
        "graphql",
        "emmet_ls",
        "prismals",
        "pyright",
        "eslint",
      },
    },
  },
}

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Mason Tool Installer: mason-tool-installer.nvim

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Auto-installed Tools

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Configuration

return {
  {
    "WhoIsSethDaniel/mason-tool-installer.nvim",
    opts = {
      ensure_installed = {
        "prettier",
        "stylua",
        "isort",
        "black",
        "pylint",
        "eslint_d",
      },
    },
  },
}

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Additional LSP Features

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LSP File Operations

• Auto-updates imports when files move
• Keeps project references in sync
• Works seamlessly with nvim-tree

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Lua Development: lazydev.nvim

• Neovim API completions
• Plugin API completions
• Better type checking for Neovim Lua

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How Completion Works

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The Flow

1. Type in Insert Mode
   • nvim-cmp monitors your typing
2. Sources Queried
   • LSP asked for completions
   • LuaSnip checks for matching snippets
   • Buffer scanned for matching text
   • Filesystem checked for path completions
3. Results Combined
   • All sources return their results
   • Results ranked by relevance
   • Icons added by lspkind
4. Menu Displayed
   • Completion menu appears
   • Navigate with <C-j> / <C-k>
   • Documentation shown in preview window
5. Completion Confirmed
   • Press <CR> to confirm
   • Text inserted at cursor
   • If snippet, placeholders activated

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Keybindings Summary

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Completion

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LSP (defined elsewhere)

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Troubleshooting

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Completion Not Working

1. Check LSP is attached: :LspInfo
2. Check sources are configured: :CmpStatus
3. Verify server is installed: :Mason

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Missing Snippets

1. Ensure friendly-snippets is installed
2. Check LuaSnip loaded: :lua print(require('luasnip').get_snippets())

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Server Not Starting

1. Open Mason: :Mason
2. Install server if missing
3. Check logs: :LspLog

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Customization

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Add More LSP Servers

ensure_installed = {
  "ts_ls",
  "rust_analyzer",  -- Add Rust
  "gopls",          -- Add Go
  -- ... more servers
}

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Change Completion Keybindings

mapping = cmp.mapping.preset.insert({
  ["<Tab>"] = cmp.mapping.select_next_item(),  -- Use Tab
  ["<S-Tab>"] = cmp.mapping.select_prev_item(), -- Use Shift-Tab
  -- ... customize more
})

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Add Custom Snippets

{
  "console.log": {
    "prefix": "cl",
    "body": ["console.log($1);"],
    "description": "Console log"
  }
}

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Related Documentation